JP2004302914A - Mass flow controller equipped with sensor for primary side pressure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mass flow controller capable of controlling a stable flow rate without being affected by pressure fluctuation in a primary side. <P>SOLUTION: This mass flow controller 10 comprises a base 20, a valve part 30, a bypass part 40 and a thermal flow rate sensor part (flow rate sensor part) 50, and a pressure sensor 110 is provided on the upstream side of the valve part 30, so that the valve part 30 is controled on the basis of not only a flow rate detected by the flow rate sensor part 50 but also primary side pressure detected by the pressure sensor 110. The base 20 is provided with fluid passages 22 and 24, an upstream side joint 26 connected to the primary side and a downstream side joint 28 connected to a secondary side. Disturbance in flow rate control caused by the pressure fluctuation in the primary side is suppressed by applying a correction operation to the flow rate control of the valve part 30 in accordance with a value detected by the pressure sensor 110. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention belongs to the technical field of a mass flow controller used in a semiconductor manufacturing process or the like.
[0002]
[Prior art]
FIG. 12 is a front view showing a part of a conventional typical mass flow controller 100 in a cross section (for example, see Patent Document 1).
[0003]
The mass flow controller 100 includes a base 20, a valve unit 30, a bypass unit 40, and a thermal flow sensor unit (flow sensor unit) 50.
The base 20 is provided with fluid passages 22 and 24, an upstream joint 26 connected to a primary side (not shown), and a downstream joint 28 connected to a secondary side (not shown). I have.
The valve section 30 is provided downstream of the bypass section 40 and the thermal flow sensor section 50.
The valve section 30 often includes an electromagnetic valve or a piezo valve (not shown) having a valve head and a valve seat.
[0004]
The gas whose flow rate is controlled in such a mass flow controller 100 is supplied from the primary side through the upstream joint 26, flows through the bypass part 40 at a predetermined ratio, then joins again on the downstream side, and joins downstream. The power is output to the secondary side via the side joint 28.
Therefore, by detecting the mass flow rate of the gas flowing through the thermal flow rate sensor unit 50, the mass flow rate of the entire gas can be known.
The detection result of the thermal flow sensor unit 50 is fed back to the valve unit 30, whereby the valve unit 30 is driven and the mass flow controller 100 is controlled.
[0005]
The thermal flow sensor unit 50 includes a heat-sensitive coil (not shown) wound on the upstream side and the downstream side.
In the thermal flow sensor unit 50 having the above-described configuration, a temperature difference due to heat transfer generated in the heat-sensitive coil is regarded as a change in electric resistance, and an unbalanced voltage is generated in the bridge circuit by the change in electric resistance. The mass flow rate of the gas that is divided at a certain rate and passes through the bypass unit 40 is detected.
[0006]
[Patent Document 1]
JP 2000-322129 A
[Problems to be solved by the invention]
As described above, in the conventional mass flow controller, the valve section is on the secondary side of the flow sensor section, and the pressures of the flow sensor section and the bypass section are continuously connected to the primary pressure. Therefore, even if the primary pressure changes due to some external factor, and the change in the pressure propagates to the pressure of the flow sensor unit and the bypass unit, and the gas flow flowing through the flow sensor unit is disturbed, the flow rate of the valve unit is changed. There is a problem that it cannot be controlled because it is downstream of the sensor section and the bypass section.
[0008]
For example, if a constant flow rate is controlled and the primary side pressure increases due to an external factor, the gas flow rate flowing to the flow rate sensor section increases accordingly, and the output signal of the flow rate sensor section increases upon detection of this. . The valve section receives the output signal of the flow rate sensor section that has increased sharply due to the primary-side pressure fluctuation, and operates to reduce the gas flow rate in order to maintain a constant flow rate. However, since the gas fluid is compressible, the gas continues to flow away from the control of the valve unit until the pressure state of the flow sensor unit and the bypass unit changed by the increase in the primary pressure becomes equilibrium. .
[0009]
[Means for Solving the Problems]
The present invention has a valve section on the upstream side of the flow sensor section and the bypass section,
Further, a pressure sensor is provided on the upstream side of the valve section,
The mass flow controller according to claim 1, wherein a correction operation is performed on the flow rate control of the valve unit based on the primary pressure detected by the pressure sensor, thereby suppressing disturbance in the flow rate control due to fluctuation in the primary pressure. Was solved.
[0010]
[Action]
According to the present invention, it is possible to suppress the disturbance of the flow rate control due to the pressure fluctuation on the primary side by adding a correction operation to the flow rate control of the valve section according to the detection value of the pressure sensor.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a front view showing a part of a mass flow controller 10 of the present invention in a cross section.
The mass flow controller 10 includes a base 20, a valve unit 30, a bypass unit 40, and a thermal flow sensor unit (flow sensor unit) 50. A pressure sensor 110 is provided upstream of the valve unit 30 and is detected by the flow sensor unit 50. The control of the valve section 30 is performed based on not only the flow rate but also the primary pressure detected by the pressure sensor 110.
The base 20 is provided with fluid passages 22 and 24, an upstream joint 26 connected to a primary side (not shown), and a downstream joint 28 connected to a secondary side (not shown). I have.
[0012]
The gas whose flow rate is controlled is supplied from the primary side via the upstream joint 26, flows through the bypass portion 40 at a predetermined ratio, and then joins again on the downstream side.
The mass flow controller 10 having the above-described configuration detects the primary-side pressure fluctuation with the pressure sensor 110 provided on the upstream side of the valve unit 30, and detects the mass flow rate of the gas flowing through the bypass unit 40 with the flow rate sensor unit 50, respectively. Then, the valve unit 30 is driven based on these values to control the gas flow rate.
By such flow control, disturbance in flow control due to pressure fluctuation on the primary side can be suppressed.
[0013]
The configurations of the valve unit 30, the bypass unit 40, and the thermal flow sensor unit 50 provided in the mass flow controller 10 are the same as those of the related art, and a description thereof will be omitted.
[0014]
An embodiment of the flow rate control will be described with reference to FIG.
In this control circuit, the detected flow rate is converted into an electric signal by the flow rate sensor unit, the signal level is adjusted by the amplifier, and the time constant of the flow rate sensor unit is adjusted. Then, the electric signal of the flow rate is compared with a set signal by a comparator, and the opening degree of the valve section is adjusted so that the set value and the electric signal of the flow rate are matched to control the flow rate.
[0015]
On the other hand, the primary pressure is converted into an electric signal by a pressure sensor upstream of the valve section, and the signal level is adjusted by an amplifier. Then, only the AC component of the electric signal representing the pressure value is taken out and added to and subtracted from the electric signal representing the flow rate. With the mass flow controller having such a configuration, when the primary side pressure fluctuates and the pressure rises while controlling a constant flow rate, only the AC electric signal of the pressure indicating the fluctuation is added to the flow rate signal, Conversely, when the pressure decreases, only the AC electric signal of the pressure representing the fluctuation is subtracted from the flow rate signal, so that a correction operation can be added to the valve section for the control disturbance caused by the primary-side pressure fluctuation. In addition, when the primary pressure is constant, the AC component of the pressure signal representing the primary pressure fluctuation becomes zero, so that the flow control is performed by comparing only the flow signal with the setting signal.
[0016]
The effect of the present invention was verified using the control circuit shown in FIG.
The control circuit is provided with a changeover switch. When the changeover switch is connected to AC, flow control is performed by comparing the flow signal with the setting signal. When the changeover switch is connected to BC, the pressure signal is changed. Is added to the control of the valve section.
Using this control circuit, control is performed to make the flow rate constant, and the flow rate control is performed by comparing the amplitude of the flow rate output due to control disturbance when the same primary-side pressure fluctuation occurs, by comparing the flow rate signal with the setting signal. And the case where the flow rate control was performed by adding the pressure signal to the control of the valve section was measured.
The respective results are shown in FIGS.
[0017]
According to these results, the amplitude when the flow rate control is performed by comparing the flow rate signal and the setting signal is 1.76 times the amplitude when the flow rate control is performed by adding the pressure signal to the control of the valve unit. It was confirmed that.
For this reason, a mass flow having a configuration in which the valve section 30 for controlling the flow rate is provided upstream of the flow sensor section 50 and the bypass section 40 as shown in FIG. 1 and the pressure sensor 110 is further provided upstream of the valve section 30 It has been confirmed that when the controller 10 controls the constant flow rate and the primary-side pressure fluctuation occurs, the controller 10 is hardly affected by the primary-side pressure fluctuation.
[0018]
In the flow control shown in FIG. 3, if a differentiation is performed when extracting the AC component of the pressure signal, it is possible to anticipate the primary-side pressure fluctuation and add a correction operation to the flow control of the valve section. Further, by selectively extracting the frequency of the AC component of the pressure signal, it is possible to use a mass flow controller that is only resistant to pressure fluctuation on the primary side in a specific cycle.
[0019]
In the above embodiment, only the AC component of the pressure signal is taken out and added to and subtracted from the flow signal. However, depending on the application, the AC component and the DC component of the pressure signal are taken out in parallel to control the valve section. It is also possible to add a correction operation.
In this case, the DC component of the pressure signal is also added to and subtracted from the flow signal. Therefore, even if the primary pressure is constant, for example, if the primary pressure is used at 100 KPa gauge pressure, the pressure value becomes Is added to the flow signal, and the opening of the valve section is adjusted so that the set value is equal to “pressure signal value + flow signal value”. Therefore, the pressure signal value in this case is “set value−flow signal value”.
[0020]
Further, as shown in FIG. 5, a pressure indicator (display means) for displaying the primary pressure value at a position which can be confirmed from the outside, or a means for outputting the primary pressure value as a pressure signal is provided. It is possible to visually check whether gas is supplied at an appropriate primary pressure to the mass flow controller, and by wiring so as to receive the pressure signal, the gas is supplied to the mass flow controller even at a distance from the mass flow controller The primary pressure can be checked.
[0021]
As described above, when a valve section is provided upstream of the flow sensor section and the bypass section, and a pressure sensor is provided upstream of the valve section to constitute a mass flow controller resistant to pressure fluctuation on the primary side, the flow sensor section and the bypass section are The pressure is continuously connected to the secondary pressure of the mass flow controller. When the secondary pressure fluctuates in the mass flow controller having such a configuration, the change is propagated to the gas flowing through the flow sensor and the bypass, and the flow output of the mass flow controller is disturbed. Further, as the secondary pressure decreases from atmospheric pressure to 500 (Torr) or less, the flow dividing ratio between the flow sensor unit and the bypass unit changes. An error occurs between the control flow rate value of the controller and the actual flow rate value.
[0022]
In order to reduce the influence of such secondary pressure, it is preferable to provide an orifice 60 in the mass flow controller 10 on the downstream side of the bypass unit 40 and the flow rate sensor unit 50 as shown in FIG. Reference numeral 70 is a seal.
The diameter of the orifice 60 depends on the critical expansion condition, that is, the ratio (P2 / P1) of the absolute pressure P1 of the gas flowing through the orifice 60 upstream of the orifice to the absolute pressure P2 downstream of the orifice is about 1/2. It is set so as to satisfy the condition that the flow velocity of the gas becomes smaller and the flow velocity of the gas passing through the orifice 60 becomes equal to the speed of sound.
[0023]
It is known that when the above condition is satisfied, the pressure fluctuation downstream of the orifice is not propagated upstream.
According to the mass flow controller 10 having such an orifice 60, fluctuations in the secondary pressure are not propagated to the bypass section 40 and the flow rate sensor section 50, so that the flow rate of gas output by the mass flow controller 10 does not fluctuate. .
[0024]
Further, in such a mass flow controller 10, since the pressure of the bypass unit 40 and the flow sensor unit 50 is higher than the secondary pressure by an amount corresponding to the pressure loss of the orifice 60, the flow error when the secondary pressure is reduced is reduced. Can be reduced.
[0025]
Using the mass flow controller 10 of the present invention shown in FIG. 2, the error in the control flow rate when the secondary pressure was reduced from atmospheric pressure to 1 (Torr) or less was measured, and the result is shown in FIG.
For comparison, a similar experiment was performed for a case where a nozzle or an orifice was not provided downstream of the bypass section and the flow rate sensor section shown in FIG. 1, and the results are also shown in FIG.
As shown in FIG. 8, according to the mass flow controller 10 of the present invention, the error when the secondary pressure was reduced to 1 (Torr) or less from the atmospheric pressure was about 0.2%.
On the other hand, as a result of performing the same experiment in the case where the nozzle or the orifice was not provided downstream of the bypass part and the flow sensor part, the error reached 6%.
[0026]
Next, the influence of the fluctuation of the secondary pressure on the output flow rate of the mass flow controller 10 of the present invention was measured.
FIG. 9 shows a configuration for performing the above-described measurement, in which the mass flow controller 10 of the present invention and the auxiliary mass flow controller M are connected in parallel, and the secondary flow is changed by changing the flow rate of gas flowing through the auxiliary mass flow controller M. The pressure P2 is varied, and the output flow rate of the mass flow controller 10 of the present invention at this time is observed with an oscilloscope O1.
The oscilloscope indicated by O2 in the figure is for observing the output of the auxiliary mass flow controller M.
[0027]
In this configuration, when the flow rate of the auxiliary mass flow controller M is changed from 0% to 100%, the secondary pressure P2 increases from 20 (Torr) to 100 (Torr), and the flow rate of the auxiliary mass flow controller M increases from 100%. When it is changed to 0%, the secondary pressure P2 falls from 100 (Torr) to 20 (Torr).
The orifice of the mass flow controller 10 of the present invention used for this measurement has a hole diameter such that the primary pressure of the orifice becomes 760 (Torr) in absolute pressure when nitrogen (N ₂ ) flows through 50 (SCCM). Things.
In this configuration, the needle valve V is provided to adjust the fluctuation range of the secondary pressure P2 generated when the flow rate of the auxiliary mass flow controller M is changed from 100% to 0%. The purpose of this is to make it easier to obtain the data of the influence of.
[0028]
FIG. 10 shows the result of measuring the output flow rate of the mass flow controller 10 of the present invention by changing the secondary pressure P2 from 20 (Torr) to 100 (Torr) in the configuration shown in FIG.
FIG. 11 shows the result of measuring the output flow rate of the mass flow controller 10 of the present invention by changing the secondary pressure P2 from 100 (Torr) to 20 (Torr) in the configuration shown in FIG.
For comparison, the secondary pressure P2 is increased from 20 (Torr) to 100 (Torr) with the same configuration as above without providing a nozzle or an orifice downstream of the bypass unit and the flow sensor unit. FIGS. 13 and 14 show the measurement results when the pressure is reduced from 100 (Torr) to 20 (Torr).
[0029]
As shown in FIGS. 10 and 11, according to the mass flow controller 10 of the present invention, the output flow rate of the gas does not fluctuate even while the secondary pressure P2 fluctuates.
On the other hand, when no nozzle or orifice is provided downstream of the bypass unit and the flow sensor unit in FIG. 1, as shown in FIGS. 13 and 14, when the secondary pressure P2 fluctuates, the gas output flow also fluctuates. You can see that
[0030]
In the mass flow controller 10 of the present invention, a nozzle (not shown) may be provided instead of the orifice 60.
Also in this case, the critical expansion condition, that is, the ratio of the absolute pressure on the upstream side of the nozzle to the absolute pressure on the downstream side of the nozzle of the gas flowing through the nozzle is smaller than about 1/2, and the flow velocity of the gas through the nozzle is reduced. A nozzle having a hole diameter that satisfies the condition that becomes a sound speed is used.
[0031]
The hole diameter of the orifice or nozzle is a flow rate between the full-scale flow rate and the minimum flow rate of the mass flow controller, and the one that satisfies the critical expansion condition under the working pressure condition of the mass flow controller is selected according to the purpose of use. At this time, an orifice or nozzle having a different hole diameter may be prepared in advance so that it can be replaced. However, it is convenient if the hole diameter of the orifice or nozzle can be changed from the outside.
[0032]
FIG. 15 shows an example of an embodiment having an adjusting mechanism 80 capable of changing the hole diameter of the orifice or nozzle from the outside. The handle 82 is rotated from the outside while the joint portion is connected to the piping, and the orifice 90 ( A portion surrounded by a dashed-dotted circle in FIG. 15B) is adjustable to an arbitrary orifice hole diameter. In FIG. 15A, the handle 82 and the stem 84 are fixed with screws 86. Further, as shown in the figure, the bonnet 88 is fixed to the body 85 and the stem 84 by a nut 87 so as to be pressed against the body 85 and the stem 84 with a load enough to exert the sealing effect of the packing 89. The bonnet 88 is internally threaded and the stem 84 is externally threaded. When the handle 82 is rotated, the handle 82 and the stem 84 move up and down by the action of the screw. When the stem 84 moves up and down, the diameter of the passage hole of the orifice 90 formed by the taper at the tip of the stem 84 and the orifice base 92 is adjusted. After the adjustment, the stem 84 is fixed by tightening the set screw 83 into the stem 84, and the orifice hole diameter is fixed.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress the disturbance of the flow rate control due to the pressure fluctuation on the primary side by adding the correction operation to the valve unit according to the detection value of the pressure sensor. .
[0034]
Further, according to the third aspect, an orifice or a nozzle that satisfies a critical expansion condition where a flow velocity becomes a sonic velocity is provided downstream of the bypass unit and the flow rate sensor unit according to a use condition of the mass flow controller. Of the pressure fluctuations on the downstream side (two sides) can be prevented.
For this reason, even if the pressure on the secondary side fluctuates, there is an effect that stable flow control can be performed.
The output flow rate of the mass flow controller does not fluctuate even when the pressure on the secondary side is fluctuating.
Further, even when the pressure on the secondary side becomes equal to or lower than the atmospheric pressure, particularly, equal to or lower than 1 (Torr), there is an effect that an error in the output flow rate is small.
[0035]
Further, when the hole diameter of the orifice or the nozzle is configured to be changeable from the outside as in claim 4, it is not necessary to replace the orifice or the nozzle each time, and the hole diameter of the orifice or the nozzle is changed according to the use condition. There is an effect that can be changed.
[Brief description of the drawings]
FIG. 1 is a front view showing a cross section of a part of a mass flow controller of the present invention.
FIG. 2 is a front view showing a part of the mass flow controller of the present invention in cross section.
FIG. 3 is a block diagram of a flow control circuit of the mass flow controller of the present invention.
FIG. 4 is a block diagram of a flow control circuit for verifying the effect of the present invention.
FIG. 5 is a block diagram of a flow control circuit of the mass flow controller of the present invention.
FIG. 6 is a view showing a result of measuring an output flow rate of the mass flow controller of the present invention in the configuration shown in FIG. 4;
FIG. 7 is a diagram showing a result of measuring an output flow rate of a conventional mass flow controller in the configuration shown in FIG.
FIG. 8 is a view showing a result of measuring an output flow error when the secondary pressure is reduced from atmospheric pressure to 1 (Torr) or less using the mass flow controller of the present invention.
FIG. 9 is a configuration diagram for measuring the influence of a change in the secondary pressure on the output flow rate of the mass flow controller of the present invention.
FIG. 10 is a diagram showing a result of measuring an output flow rate of the mass flow controller of the present invention in a state where the secondary pressure is changed from 20 (Torr) to 100 (Torr) in the configuration shown in FIG. 9;
FIG. 11 is a diagram showing a result of measuring an output flow rate of the mass flow controller of the present invention in a state where the secondary pressure is changed from 100 (Torr) to 20 (Torr) in the configuration shown in FIG. 9;
FIG. 12 is a front view showing a cross section of a part of a conventional mass flow controller.
FIG. 13 is a view showing a result of measuring an output flow rate of a conventional mass flow controller in a state where the secondary pressure is changed from 20 (Torr) to 100 (Torr) in the configuration shown in FIG. 9;
FIG. 14 is a view showing a result of measuring an output flow rate of a conventional mass flow controller in a state where the secondary pressure is changed from 100 (Torr) to 20 (Torr) in the configuration shown in FIG. 9;
15A and 15B are cross-sectional views of an embodiment in which the hole diameter of an orifice or a nozzle can be changed from the outside. FIG. 15A is a cross-sectional view of a main part, and FIG. The enlarged sectional view of the part enclosed by.
[Explanation of symbols]
10: Mass flow controller 20: Base 30: Valve section 40: Bypass section 50: Flow rate sensor section 60, 90: Orifice 110: Pressure sensor

Claims (6)

Has a valve section on the upstream side of the flow sensor section and the bypass section,
Further, a pressure sensor is provided on the upstream side of the valve section,
By adding a correction operation to the flow control of the valve unit based on the primary pressure detected by the pressure sensor, to suppress disturbance of the flow control due to fluctuations in the primary pressure,
Mass flow controller. The mass flow controller according to claim 1, wherein the correction operation is performed by an AC component of an output of the pressure sensor. 2. The mass flow controller according to claim 1, wherein said correcting operation is performed by an AC component and a DC component of an output of said pressure sensor. 4. The mass flow controller according to claim 1, further comprising a display unit or an output unit for displaying the detected value of the primary pressure. The orifice or the nozzle is provided on the downstream side of the bypass part and the flow sensor part so as to satisfy a condition that a flow velocity of a gas passing through the orifice or the nozzle becomes a sonic velocity. Mass flow controller. The mass flow controller according to claim 5, wherein a hole diameter of the orifice or the nozzle can be changed from outside.

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